if you delete the incremental then you can't do any restores between the fulls.

so sa you follow the default schedule of full on friday and incremental ever other day. then if you delete the incrementals you can only restore the account to the point it was at on friday and not to a point like monday.

yeah the incrementals are useless without the previous full. they contain some blobs which i guess could be useful but in terms of using the zimbra restore utilities yeah they're useless.